1. Field of the Invention
The present invention relates to a method and an apparatus for manufacturing a multi-layer bottle. More specifically, the present invention relates to a method and an apparatus for manufacturing a multi-layer bottle which has a separating function.
2. Description of the Related Art
Heretofore, a multi-layer bottle has been molded in the following manner. In the first place, a multi-layer die head of a blow molding machine is used so as to make a plurality of molten resins supplied from a plurality of extruders a laminar shape. Next, each layer is joined to each other in a nozzle of the die head so as to form an integral parison. Finally, the parison is discharged between molds.
Recently, the multi-layer bottle having a separating function has been used as the bottle for a shampoo, a rinse or the like. In case of the aforementioned bottle, when contents are discharged from a pouring pump fitted to an opening of the bottle, a negative pressure is caused in the bottle. This results in a deformation of an appearance of the bottle and a difficulty in the discharge of the contents. In order to prevent this, for example, Japanese Patent Application Laid-open No. 213372/1993 proposes a multi-layer bottle 31 as shown in FIGS. 1a and 1b. A wall of a body 32 of the multi-layer bottle 31 comprises a two-layer structure: an outer layer 33 and an inner layer 34. The outer layer 33 and the inner layer 34 are formed of different resins which are not adhered to each other. A wall thickness of the inner layer 34 is thinner than that of the outer layer 33. In case of the bottle 31, when the contents are discharged and thus the inner layer 34 is shrunk, a pinch-off of the inner layer 34 is removed from a bottom portion of the outer layer 33 so that a vent hole 35 is formed on the bottom portion of the outer layer 33. The vent hole 35 is disposed in order to prevent a vacuum status which occurs when a reduction of the contents causes the inner layer 34 to be shrunk. Typically, after a molding of the multi-layer bottle, the inner layer 34 is once separated and then the vent hole 35 is formed in the outer layer 33. The thus manufactured bottle 31 appears to be integrally structured immediately after the molding due to a multi-layer molding which uses the different resins, each having no adhesivity to each other. However, whenever the contents are discharged from a pouring pump 38 fitted to an opening 37 of the bottle 31, the outer layer 33 remains while the inner layer 34 is gradually shrunk. Thus, the contents can be efficiently discharged to the end.
Since the prior art multi-layer bottle is constructed in the above-described manner, the following problems exist:
(a) when the multi-layer bottle has an inner layer separating function, the inner layer is typically thinner than the outer layer. Thus, during the molding of the parison, the circumferential wall thickness of the inner layer is subject to variation due to change in the wall thickness of the outer layer; PA1 (b) when a pinch-off portion of the molded multi-layer bottle has a multi-layer structure, more specifically, when the multi-layer bottle has the inner layer separating function, since a material having the separating function is used as an inner layer parison, a strength is weakened in the pinch-off portion; PA1 (c) since the parison is multi-layered over the total length thereof, a pinched-off burr is also multi-layered and thus it is difficult to reuse the burr; PA1 (d) when the multi-layer bottle has the inner layer separating function, it is desirable that the inner layer is crushed to a small size in order to improve dischargeability of the contents. However, typically, as shown in FIG. 1b, since a width C of inner/outer layer pinch-off is wide, the pinch-off portions presses against the inner layer and thereby the inner layer is difficult to crush. Furthermore, since the wall thickness in the periphery of the pinch-off portion has less blow ratio, the wall is thicker and thereby the inner layer is more difficult to crush. Thus, the dischargeability of the contents becomes worse; PA1 (e) when the vent hole is formed in the outer layer of the multi-layer bottle having the inner layer separating function, the formation takes a lot of time. At that time, there is a fear of the crush or deformation of the bottle body. There is arisen another problem about a removal of cutting powder which is generated when the pinch-off portion is separated and the hole is formed; and PA1 (f) when the multi-layer bottle has the inner layer separating function, during the discharge of the contents, a lower portion of the inner layer is also separated from the outer layer. Thus, the inner layer is vibrated, and therefore an outer surface of the inner layer comes into contact with an inner surface of the outer layer, thereby generating a noise.